Alt-BEAM Archive

Message #07352



To: beam@corp.sgi.com
From: Jacob Booth j.booth@mary.acu.edu.au
Date: Thu, 04 Nov 1999 11:31:40 +1100
Subject: [alt-beam] directional can of worms


There are many ways of direction finding with RF. Not necessarily easy
ones, as thing just happen too fast. No one has yet mentioned the fact that
in a beam type environment, reflections and shadow areas would be far too
common. Don't get me wrong, I am not poo-pooing the idea at all; I would
like to have a tracking station that I could use to monitor my bot's motion
on my pc (so I could see what it was up to during the day.

I have a video camera hooked up for time lapse, but that just ain't as fun
:). That would help on the size problem, as the bot would be sending out
the beacon, and the antenna system could be set around it's operating area
at a more manageable distance.

I think triangulation error would still be rather inaccurate at this kind
of scale. Finding a ship at sea would be easier than finding my bot under
the sofa :)

Maybe (and boy, am I going to open a can of worms here, and reopen some
long dead threads) the good old 40khz AUDIO transducers would be of some
use here. The 'beam' of audio is quite directional, and things happen at an
order of magnitude slower in audio. I know polaroid made some fantastic
units (complete, with transducer and driver/rx board) that we used on some
prototype bitumen laying machinery. This stuff was VERY accurate (had
temperature compensation etc) to within 1-2 mm over a 1.5 metre range. The
range was extensible, with a similar extension on the accuracy (eg 15 m
range 1-2 cm accruracy. Not bad at all really). Unfortunately they stopped
production of the unit. You can still get the transducer (they still use
them in the autofocus of their cameras) but they needed some bizzare
voltages to run (300v pulse to transmit etc). We tryed to build the driver
boards ourselves, but just couldn't copy the quality or repeatability. They
also used custom ic's :(

So what was I saying? Oh, yeah, uh, so sound can be used instead of RF in
short-range projects. PIcture 3-4 mikes around a room, hooked up to some
sort of differential op-amp stage and a pc, the bot wandering about
'barking'. And then picture the PC drawing a trace of the bot wandering
about the screen. Maybe different tones (or even DTMF) so the bot can
communicate what it is 'thinking'.

Well, thats got my two typing fingers tired.

cheers
Jacob
------------------------------------------------------------------
Jacob Booth BIS, MCP Web http://www.its.mary.acu.edu.au/
IT Services Email j.booth@mary.acu.edu.au
Phone (02) 97392235 Fax (02) 97392924
Australian Catholic University - MSM Campus Strathfield NSW



7353 Thu, 04 Nov 1999 11:47:26 +1100 [alt-beam] Tildens Window Cleaning Robots Beam Mailing List Elmo Hi all

I was reading an old issue of New Scientist (July 1988) which had an
article on Beam called "Brainless Wonders". In it Mark mentions that he
has some robots that "Clean his windows". Has anyone ever seen or heard
anything about these robots? I am curious as to how they work and more
importantly, How he gets the to traverse or stick to the glass?


Elmo

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